Flash-butt welding, or “flash welding” is a resistance welding technique for joining segments of metal rail, rod, chain or pipe in which the segments are aligned end to end and electronically charged, producing an electric arc that melts and welds the ends of the segments, yielding an exceptionally strong and smooth joint.
A flash butt welding circuit usually consists of a low-voltage, high-current energy source (usually a welding transformer) and two clamping electrodes. The two segments that are to be welded are clamped in the electrodes and brought together until they meet, making light contact. Energizing the transformer causes a high-density current to flow through the areas that are in contact with each other. Flashing starts, and the segments are forged together with sufficient force and speed to maintain a flashing action. After a heat gradient has been established on the two edges to be welded, an upset force is suddenly applied to complete the weld. This upset force extrudes slag, oxides and molten metal from the weld zone leaving a welding accretion in the colder zone of the heated metal. The joint is then allowed to cool slightly before the clamps are opened to release the welded article. The welding accretion may be left in place or removed by shearing while the welded article is still hot or by grinding, depending on the requirements.
A welded bearing ring may be subjected to a post-welding heat treatment, such as carburizing, in order to increase its surface hardness, wear resistance and/or fatigue and tensile strength. Carburizing is a heat treatment process in which an iron or steel component is heated in the presence of another material that liberates carbon as it decomposes. The outer surface of the component will have a higher carbon content than the original material. When the iron or steel component is cooled rapidly by quenching, the higher carbon content on the outer surface becomes hard, while the core remains soft (i.e. ductile) and tough.